<!DOCTYPE html>
<html>
  <head>
    <meta charset="utf-8" />
  </head>
  <body>
    <ul>
      <li>.</li>
      <li>.</li>
      <li>.</li>
    </ul>

    <script type="text/javascript">
      // 补全代码
      var ul = document.querySelector('ul')
      var lis = document.querySelectorAll('li')
      ul.addEventListener('click', (e) => {
        e.target.innerHTML += '.'
        console.log(e.target.innerHTML)
      })
    </script>
  </body>
</html>
